The present invention relates to a head gimbal assembly in a disc drive system, and more particularly to the interconnecting leads which connect the transducing head to the flexible interconnect circuit.
Disc drives are well known in the art and comprise several discs, each disc having several concentric data tracks for storing data. A transducing head is used to read from or write to a data track on a disc. As the disc is spun, the head is positioned above a data track on a disc by moving an actuator arm on which the head is suspended. The arm is moved using a large scale actuation motor, such as a voice coil motor.
The head is mounted on the actuator arm using a head gimbal assembly. A standard head gimbal assembly comprises a load beam, a gimbal, a flexible interconnect circuit, and the head. The load beam provides the main support structure for the head gimbal assembly. A gimbal is attached under the load beam, and the head is attached to the gimbal. The gimbal is designed to allow the head to follow the surface of the disc more closely than if the head were mounted directly on the load beam. The flexible interconnect circuit is laid on top of the load beam and provides the circuitry to and from the head in the form of interconnect leads. The leads connect the flexible interconnect circuit to the head and thus allow electronic signals to pass between the two.
All parts of the head gimbal assembly are constructed to accommodate high precision movement so that the head can be placed above a desired data track. In addition, the design of the head gimbal assembly must allow the head to closely follow the surface of the disc as the disk is spinning. To allow the head to do so, the gimbal and flexible interconnect must be flexible. In particular, the leads connecting the head to the flexible interconnect circuit must have low stiffness. At the same time, the leads must be robust enough to survive the manufacturing process and day-to-day use.
Typically, prior art leads have a uniform width that is kept small to ensure flexibility, but the small width also causes the prior art leads to be fragile and easily breakable. Though it is possible to widen the leads to increase their robustness, when widened the leads become too stiff and prevent the head from moving in such a manner as to be able to follow the disc surface. If the leads are made narrower, the stiffness is reduced and the head is able to achieve the desired range of motion. However, as the leads are made to be more narrow, the leads also become less robust and experience a much higher incidence of breakage. When breakage occurs, it most often happens at the point where the lead must be bent to allow the lead to be attached to the head.
In an effort to strengthen the leads and improve their robustness and resistance to fatigue, an adhesive conformal coat may be selectively placed onto the leads. However, this process is time consuming and is difficult to control. Further-more, it does nothing to address the breakage that occurs at the areas where the leads are bent.
Thus, there is a need in the art for a head gimbal assembly having interconnecting leads which are robust enough to survive the manufacturing process and use while being flexible enough to allow the head gimbal assembly to function.
The present invention relates to head gimbal assembly interconnecting leads having improved robustness and lower stiffness. The interconnecting leads are shaped so that the width of the leads varies at points where the lead is likely to break. Specifically, the width of the lead at the point it becomes unsupported by the flex circuit is made wider. The lead is also made wider at the top of the head bond pad. To insure that the pitch stiffness remains low enough to allow the head to move over the disc surface, portions of the lead are made narrower. By widening some portions of the lead and narrowing other portions of the lead, it is possible to reach a point where the lead is made much more robust, yet retains the low stiffness required for the head gimbal assembly to function properly.